Ultrathin Polymer Films: Viscoelasticity, Physical Aging and Failure

技术概述：超薄聚合物薄膜在玻璃温度以下的行为还不是很清楚，尽管它在聚合物结构的微米和纳米尺度工程中很重要。对于几种不同的聚合物材料，需要进行研究以了解超薄聚合物薄膜作为温度和薄膜厚度的函数的物理老化响应。该方法包括使用德克萨斯理工大学(TTU)实验室开发的一种新的气泡膨胀测量方法进行测量，以执行等双轴和非等双轴变形几何图形。这将是第一次对自由站立的超薄聚合物薄膜进行物理老化测量。此外，这项工作采用了一种独特的去湿方法，以便在聚苯乙烯薄膜的玻璃化转变附近进行物理老化实验。这些除湿实验提供了与纳米气泡完全不同的薄膜约束，两种方法之间的结果比较对这两种技术提出了强大的挑战，这两种技术名义上相似，但在文献中给出了不同的和迄今为止不一致的结果。这项工作还直接探索了受限聚合物的动力学，并解决了文献中报道的中尺度和纳米尺度的不可调和老化反应。最后，纳米尺度的材料失效还很少被研究，TTU气泡膨胀技术将被用来检测超薄聚合物薄膜的断裂行为。非技术摘要：聚合物在微电子领域得到了广泛的应用，现在已经成为纳米电子应用。由于观察到当特征尺寸小于100 nm时，聚合物材料的性能发生变化，这使得电子开发者和设计者很难在纳米尺度上设计和预测聚合物的行为。类似的效应也出现在纳米复合材料和其他纳米级聚合物的未来应用中。本工作旨在将两种不同的纳米尺度性质的测量方法直接对峙，以协调文献中已报道的纳米尺度性质的差异。一种方法是由德克萨斯州卢伯克的首席研究员开发的TTU纳米气泡充气测试，另一种是由佛罗里达州巴黎的ES.P.C.I.的研究人员开发的纳米膜去湿方法。这项工作的结果将为在纳米尺度上报告材料行为相似和不同的原因提供非常重要的见解。除了技术工作外，这项研究还将由TTU化学工程实验室的研究生进行，将为两名学生提供培训机会，并完成大部分研究教育，以获得博士学位。最后，研究结果将通过期刊出版和由国际和平协会和学生在全国会议上发表的报告来广泛传播。

TECHNICAL SUMMARY:The behavior of ultrathin polymer films below the glass temperature is not well understood despite its importance in micro- and nano-scale engineering of polymeric structures. Research is to be performed to understand the physical aging response of ultrathin polymer films as a function of temperature and of film thickness for several different polymeric materials. The approach includes making measurements using a novel bubble inflation method of measurement developed in the labs of Texas Tech University (TTU) to perform equi-biaxial and nonequibiaxial deformation geometries. These will be the first physical aging measurements on freely standing ultrathin polymer films. In addition, the work adapts a unique dewetting method in order to perform physical aging experiments below but near to the glass transition for polystyrene films. These dewetting experiments provide completely different film constraint than do the nanobubbles and comparison of the results between the two methods provides a strong challenge to both techniques that are nominally similar, but in the literature have given different and, to-date, unreconciled results. The work also directly probes the dynamics of confined polymers and addresses unreconciled mesoscale vs. nanoscale aging responses that have been reported in the literature. Finally, material failure at the nanometer size scale has been little investigated and the TTU bubble inflation technique will be exploited to examine the rupture behavior of ultrathin polymer films.NON-TECHNICAL SUMMARY:Polymers are widely used in micro-, now becoming nano-, electronics applications. Because it is observed that polymer material properties change when feature sizes are smaller than 100 nm, this makes design and prediction of the polymer behavior at the nanoscale difficult for the electronics developer and designer. Similar effects occur in nanocomposites and other futuristic applications of polymers at the nanoscale. The present work is designed to put two different methods of measurement of nanoscale properties into direct confrontation in order to reconcile differences of nanoscale properties that have been reported in the literature. One method is the TTU nanobubble inflation test developed by the principal investigator in Lubbock, TX and the other is a nanofilm dewetting method developed by researchers at the E.S.P.C.I. in Paris, FR. The outcome of the work will provide highly important insights into the reasons for similarities and differences in reported material behaviors at the nanometer size scale. In addition to the technical work the research is to be carried out by graduate students in the Chemical Engineering Laboratories at TTU and will provide opportunities for two students to be trained and to achieve the bulk the research education to obtain their Ph.D. degrees. Finally, the results of the research will be widely disseminated through journal publication and presentations by the PI and students at national meetings.